Set out a blender. Place the onion wedges, tomato wedges, piece of ginger, garlic cloves, and peanut butter in the blender. Cover and purée until smooth.
Set a large soup pot over medium heat. Pour the peanut butter purée into the pot. Stir in the broth, chicken breast pieces, chopped bell pepper, carrots, and crushed red pepper. Add 1 teaspoon of salt. Stir well and bring to a low boil.
Simmer for 20 to 25 minutes, until the chicken is cooked through. Stir it regularly to make sure the chicken and veggies do not stick to the bottom of the pot.
Taste, then season with salt and pepper as needed. Serve as is, or with a side of rice.